h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Here todays

In Hawaii, if you drop a steel ball weighing five pounds from a height
of 45
inches, will it fall more rapidly through water at 20 degrees
Fahrenheit or
water at 40 degrees Fahrenheit. Or will it make no difference... and
why?

If the water is 20 degrees Fahrenheit, it's probably frozen, so the ball won't fall through it at all, so 40 degrees is the answer.

*almost* a simpost

Of course cloughie are right!

I just got lucky, I usually sleep another hour or so!

Didn't think there had been a good freeze in Hawaii since the last ice age...

It will make no difference. Grabity is Grabity and the rate of descent, or fall, is the same.

And yes water can still be in a liquid state at 20 degress F.

Otherwise, yeah, what he said.

...especially if that water's been polluted with anti-freeze!

Ah ha! The problem with this arguement is that you forgot about viscosity!

The force on the ball due to gravity is the same at the same place, yes, but the viscosity of water is temperature-dependent (the viscosity of pure water increases near the freezing point - for highly compressed water under extreme conditions [i.e. liquid at 20F] one would expect the viscosity to be very high relative to water at 40F). Viscosity would affect the frictional force acting on the steel ball as it moved through the water making it move slower through the colder water. Viscosity is not a constant like the force of gravity in this case. Salt water viscosity would also depend on temperature. I assume we're talking about salt water, as it's almost the only way you'd find liquid water at 20F at Hawaii (i.e. near the bottom of the Ocean at one of the deep trenches where hideous pressure and cold temperatures prevail, as long as you're not near any volcanic vents, of which there are plenty).

I think the question meant to point out that water is typically solid at 20F, particularly fresh water, and most assuredly at standard pressure - a steel ball will not pass through solid water as fast as it would through liquid water with just gravity acting on a 5-lb ball falling from 45" being the only driving force. Even if you had some kind of highly pressurized liquid water at 20F as you conducted this test, it would fall through the colder, denser water more slowly. The same applies to salt/sea water. Of course, if we're talking about highly polluted water or water with some significant amounts of certain chemicals (like antifreeze) added, then my arguement is moot as it isn't really water, is it?

Didn't forget viscosity factors just didn't want to go into it and was fairly certain it wasn't a factor in the answer and since I don't know if GTC will go thru all of these when she gets back felt it wasn't worth the effort to try for a fractional point on the question.The question of water w/anti-freeze or other things in it has some conections w/viscosity and surface tension, etc. Too many to try to figure out today.
Ta.

Besides, the only place you're likely to find water at 20 degress and 40 degress at the same place is a water glass or a punch bowl and I'm fairly certain dropping a 5 lb. iron ball in either of them is going to get you in much hotter water than is comfortable. (teehee)

In the immortal words of Monty Phython:"run away, run away, run away".

I thought that was the teletubbies...

jr...drop by Lil's!

The temperature of the steel ball makes no difference.

Nor does the temperature of the air. Of course if you drop the steel ball into the water and is your BODY temperature that is 20 degrees (or 40 degrees), the question is moot since you cannot observe the result.

Viscosity not withstanding.

so I was correct, right?

Well done cloughie... nice and correct... ~grin~